The Uptake of Mercury and Relationship to Food Habits of Target Fish Species in the South River and South Fork Shenandoah River
G. Murphy, T. Newcomb, and D. Orth Department of Fisheries and Wildlife Sciences Virginia Tech Virginia Tech Study
OBJECTIVE 1: • Determine diet composition of the target fish species in study and references reaches
Asian clam Darter Target Fish Species
White sucker Smallmouth bass
Channel catfish Redbreast sunfish Study Reaches
• South River: - Waynesboro to Port Republic
• South Fork Shenandoah River:
- Port Republic to Front Royal South River
• North River (reference):
- Port Republic to Bridgewater
South Fork Fish Sampling Sites
Shenandoah River
North Fork
South Fork North River N
Middle River
Contamination Point South River
0 30 60 miles Fish Collection Methods
• Boat & barge electrofishing • Hoop netting • Goal = 30/species/reach • Maximize age/size range • Seasonally Fish Processing Methods
• Fish identification • 40-80 ppm clove oil anesthetic • Measured TL (mm) • Weighed (g) • Sexed Fish Processing Methods
• Stomach or intestine:
- 10% formalin - diet analysis • Otoliths (earstones):
- age analysis Laboratory Methods
• Food item identification: - invertebrates (order) - fish (species) • Blotted dry • Weighed to 0.001g • Stored in 70% ethanol Fish Collection Results April + July
CCF RDB SMB WHS South - 66 77 70 River South 39 74 80 60 Fork North - 54 61 60 River Totals 39 194 218 190 641
South Fork Channel Catfish Preliminary Findings South Fork Channel Catfish
90% April July 80% 70% 60% 50% 40% 30%
Percent by Weight (g) by Weight Percent 20% 10% 0%
Food Item South Fork Channel Catfish Fish Analysis
60% April July
50%
40%
30%
20% Percent by Weight (g) by Weight Percent 10%
0% PDUF Redbreast Sunfish Smallmouth Sunfish Bass Food Item South Fork Channel Catfish Summary
• Mainly consume sunfishes (centrarchids) in April & July • Green algae important in July • Opportunistic feeders: - meadow vole - crayfish -fish - green algae - aquatic insects White Sucker Preliminary Findings White Sucker April
South River South Fork North River 70% 60% 50% 40% 30% 20%
Percent by Weight (g) by Weight Percent 10% 0%
Food Item White Sucker Insect Analysis
South River South Fork North River 60% 50% 40% 30% 20% 10% Percent by Weight (g) by Weight Percent 0%
Food Item White Sucker Summary
• Mainly consume aquatic insects: - Ephemeroptera (North River) - Trichoptera (South Fork) - Diptera (South River) • Large amount of unidentifiable organic matter • Mollusca important in South Fork
Diptera Redbreast Sunfish Preliminary Findings Redbreast Sunfish < 126 mm
South River South Fork North River 100%
80%
60%
40%
Percent by Weight (g) by Weight Percent 20%
0%
Food Item Redbreast Sunfish 126 - 150 mm
100% South River South Fork North River
80%
60%
40%
20% Percent by Weight (g) by Weight Percent
0%
Food Item Redbreast Sunfish 151 - 175 mm
100% South River South Fork North River
80%
60%
40%
20% Percent by Weight (g) by Weight Percent
0%
Food Item Redbreast Sunfish > 175 mm
South River South Fork North River 100%
80%
60%
40%
20% Percent by Weight (g) by Weight Percent
0%
Food Item Redbreast Sunfish Insects Analysis
60% South River South Fork North River 50% 40% 30% 20%
Percent by Weight (g) by Weight Percent 10% 0%
Food Item Redbreast Sunfish Summary
• Mainly consume aquatic insects • Larger cohorts have a more variable diet • Larger cohorts shift to terrestrial insects from April to July • Ephemeroptera, trichoptera, and diptera most common • Decrease in ephemeroptera and increase in trichoptera from April to July in all reaches
Trichoptera Smallmouth Bass Preliminary Findings Smallmouth Bass < 100 mm
South River South Fork North River 100%
80%
60%
40%
Percent by Weight (g) by Weight Percent 20%
0%
Food Item Smallmouth Bass 100 - 199 mm
100% South River South Fork North River
80%
60%
40%
Percent by Weight (g) by Weight Percent 20%
0%
Food Item Smallmouth Bass 200 - 299 mm
South River South Fork North River 100%
80%
60%
40%
Percent by Weight (g) by Weight Percent 20%
0%
Food Item Smallmouth Bass > 299 mm
100% South River South Fork North River
80%
60%
40%
Percent by Weight (g) by Weight Percent 20%
0%
Food Item Smallmouth Bass Fish Analysis
70% South River South Fork North River 60% 50% 40% 30% 20% Percent by Weight (g) by Weight Percent 10% 0%
Food Item Smallmouth Bass Summary
• < 100 mm cohort mainly consuming aquatic insects • Smaller cohorts in South River consuming more fish • Larger cohorts consume mostly crayfish and fish • Larger cohorts consume more crayfish and less fish from April to July
• Fish species consumed differ
Crayfish Final Summary
• Diet results agree with literature review • Good representation from each trophic group • Fish, aquatic insects, and crayfish are most commonly consumed
Shiner Plecoptera Crayfish Upcoming Events
• October fish sampling event (14 of 16 completed) - sample final 2 sites on North River tomorrow • December fish sampling event • Continue diet and age analysis
South Fork Acknowledgements
Committee Members: Steve Reeser Tammy Newcomb Don Cherry Don Orth John Ney
South River Science Team Questions?